Nuclear receptors are a family of small molecule and hormone-regulated transcription factors that share conserved DNA-binding and ligand-binding domains. Small pharmacological compounds able to bind to the cleft of the ligand-binding domain could alter its conformation and subsequently modify transcription of target genes. Such ligand agonists and/or antagonists have already been successfully designed for 23 nuclear receptors among the 48 previously identified in the human genome (1-3). RORalpha (ROR ; RORA; NR1F1) is one of three related orphan nuclear receptors, including RORbeta (ROR ; RORB; NR1F2) and RORgamma (RORg; RORC; NR1F3), known as "Retinoic Acid Receptor-related orphan receptors" (4).

RORA has unusual potential as a therapeutic target for the "metabolic syndrome" which results in pathologies such as insulin resistance, dyslipidemia, hypertension, and a pro-inflammatory state, that greatly elevates the risk of diabetes and atherosclerosis (5).The related RORC demonstrates significant expression in metabolic tissues such as liver, adipose, and skeletal muscle (6). These two receptors are implicated in several key aspects of this metabolic pathogenesis. For instance, the staggerer mouse, which carries a homozygous germline inactivation of RORA, shows low body weight, high food consumption (7-9), elevated angiogenesis in response to ischemia (10), susceptibility to atherosclerosis (9), and an abnormal serum lipid profile (11). RORG null mice exhibit normal plasma cholesterol levels, but when bred with the RORA staggerer mice, the resulting RORalpha/gamma knockout exhibits hypoglycemia not found in the single mutant animals. These studies reveal the functional redundancy of RORa and RORg in regulating blood glucose levels and highlight the need for RORalpha/gamma ligands that can bind to these receptors and modulate their transcriptional activity (12,13).

The purpose of this assay is to determine whether powder samples of test compounds identified as possible RORA inverse agonist probes are nonselective due to inhibition of RORG. This assay employs the RORg-expressing cell line from a GAL4 nuclear receptor library. In this assay, HEK293T cells cotransfected with a GAL4DBD-RORgLBD construct (GAL4-RORg) and a GAL4UAS-luciferase reporter construct are incubated for 18-24 hours with test compounds. The presence in this cell line of required co-activators allows the expression of luciferase driven by activated RORg nuclear receptors. As designed, compounds that inhibit RORg activity will prevent activation of the GAL4-RORg construct, thereby preventing GAL4DBD mediated activation of the GAL4UAS-luciferase reporter, leading to a decrease in well luminescence. Compounds were tested at a nominal concentration of 10 uM. Six replicates were performed for each assay.

Protocol Summary:

Luciferase reporter assays were conducted using a pBind GAL4DBD-RORgLBD construct and UAS luciferase reporter cotransfected into HEK293T cells. Reverse transfections were performed in bulk using 4E6 cells in 10 cm plates, 9 ug of total DNA and FuGene6 (Roche) in a 1:3 DNA: lipid ratio. Following 24 hour bulk transfection, cells from were counted and re-plated in 384 well plates at a density of 10,000 cells/well. Following 4 hour incubation, cells were treated with DMSO/compounds for 20 hours. The luciferase levels were measured by addition of BriteLite Plus (Perkin Elmer). Data was normalized to luciferase signal from DMSO treated cells.

The fold-change inhibition for each compound was calculated as follows:

This assay was performed by the assay provider. This assay may have been run as two or more separate campaigns, each campaign testing a unique set of compounds. In this case the results of each separate campaign were assigned "Active/Inactive" status based upon that campaign's specific compound activity cutoff value. All data reported were normalized on a per-plate basis. Possible artifacts of this assay can include, but are not limited to: dust or lint located in or on wells of the microtiter plate, or compounds that modulate well luminescence. All test compound concentrations reported above and below are nominal; the specific test concentration(s) for a particular compound may vary based upon the actual sample provided.